Add semicolon to "Maybe a missing extern crate foo" message

src/librustc_resolve/lib.rs

@@ -1412,7 +1412,7 @@ impl<'a> Resolver<'a> {
 
                                 format!("Did you mean `{}{}`?", prefix, path_str)
                             }
-                            None => format!("Maybe a missing `extern crate {}`?", segment_name),
+                            None => format!("Maybe a missing `extern crate {};`?", segment_name),
                         }
                     } else {
                         format!("Could not find `{}` in `{}`", segment_name, module_name)

src/test/compile-fail/issue-12612.rs

@@ -16,7 +16,7 @@ use foo::bar;
 
 mod test {
     use bar::foo; //~ ERROR unresolved import `bar::foo` [E0432]
-                  //~^ Maybe a missing `extern crate bar`?
+                  //~^ Maybe a missing `extern crate bar;`?
 }
 
 fn main() {}

src/test/compile-fail/issue-1697.rs

@@ -11,6 +11,6 @@
 // Testing that we don't fail abnormally after hitting the errors
 
 use unresolved::*; //~ ERROR unresolved import `unresolved::*` [E0432]
-                   //~^ Maybe a missing `extern crate unresolved`?
+                   //~^ Maybe a missing `extern crate unresolved;`?
 
 fn main() {}

src/test/compile-fail/unresolved-import.rs

@@ -11,7 +11,7 @@
 // ignore-tidy-linelength
 
 use foo::bar; //~ ERROR unresolved import `foo::bar` [E0432]
-              //~^ Maybe a missing `extern crate foo`?
+              //~^ Maybe a missing `extern crate foo;`?
 
 use bar::Baz as x; //~ ERROR unresolved import `bar::Baz` [E0432]
                    //~^ no `Baz` in `bar`. Did you mean to use `Bar`?